International Wine Technical Summit, 2017 Harmonizing Expression of Measurement Results in Wine Analysis: Best Practices When Testing and Reporting Sugar in Wine International Wine Technical Summit, 2017 M. Sarita Cardozo Chemist Compliance Laboratory Scientific Services Division Alcohol and Tobacco Tax and Trade Bureau Walnut Creek, CA

Summary This paper proposes the following best practices: Clarify abbreviation ‘RS’ when used. Express residual sugar as sum of glucose, fructose and sucrose in g/L of wine. Use test methods specific for wine sugars. Avoid reporting sugar alcohols, such as glycerol, as a sugar. Avoid testing for sugars not expected in wine.

Background Paper developed in response to: Dialog among past IWTS participants Trade problems due to sugar results from different methodologies Observed results for sugars in the 2015 APEC Wine Regulatory Forum Ring Test

2015 APEC WRF Ring Test Results - Sugars in Red Wine Method N (APEC) APEC Mean (g/L) APEC (%CV) N (IWAG) IWAG Mean (g/L) IWAG (%CV) Reducing Sugars 12 4.51 ± 1.39 29 42 4.34 ± 0.8 18 Glucose+Fructose 10 2.24 ± 0.53 24 110 2.3 ± 0.41

Why is this a problem? Some economies have sweetness labeling standards: - Dry: Max of 4 g/L - Medium dry: 4 – 12 g/L - Semi-sweet: 12 – 45 g/L - Sweet: > 45 g/L Sugar-free extract calculated from erroneously high sugar results are erroneously low. Trade has been impacted by these labeling issues.

Sugar Composition in Wine Typical sugar composition: - glucose + fructose = 95% - sucrose 3% - pentoses and other sugars 2% Not expected: - maltose - lactose Sugar alcohols are not sugars: - glycerol For wine: Residual sugar (RS) refers to sum of glucose + fructose + sucrose

What is ‘RS’? Reducing Sugar Residual Sugar Reducing Substance Sugar with an aldehyde or keto group Fermentable sugars Any substance than can reduce copper ions in solution Glucose & fructose Glucose & fructose Pentoses (non-fermentable) Sucrose Oligosaccharides Tannins & polyphenols

Sugar Methods Sugar specific methods HPLC – fructose, glucose and sucrose Enzymatic – fructose, glucose (and sucrose as glucose) FTIR Non-specific methods reducing sugar methods (Lane-Eynon and Rebelein) over estimate sugars content interference from non-sugar reducing substances present in wine (tannins & polyphenols) Note : Sugar-free extract values calculated from erroneously high sugar results are erroneously low.

Summary Conclusions Clarify the meaning of ‘RS’ when used. Report residual sugar as sum of glucose, fructose, and sucrose in g/L wine. Use methods specific for wine sugars, avoid those that also test for reducing substances. Avoid reporting sugar alcohols, such as glycerol, as a sugar. Avoid testing for sugars not expected in wine - maltose - lactose